The objective of the proposed study is to investigate the conditions under which various compounds might create a differential radiosensitivity between normal and malignant tissues of the laboratory mouse, so that the potential of these compounds for clinical radiotherapy can be evaluated. The investigation is specifically designed to have relevance to the clinical treatment of cancer; first, by choosing criteria of radiation damage which are directly analogous to the late effects in humans which limit the radiation dose--necrosis of connective tissue, pneumonitis, nephritis, myelitis and hepatitis; second, by choosing cure as the main endpoint for the tumors; and third, by concentrating the investigation on fractionation schedules close to those used clinically--10 daily fractions and 20 and 30 fractions delivered 5 times weekly. Four different transplantable tumors will be used so as to cover a wide range of histologic types and to make use of the various advantages of each. These will be the KHT sarcoma and the MDAH-MCa4 mammary carcinoma in C3H mice, the EMT6 tumor in BALB/c mice, and the brain-implanted SK-26 glioma in C57BL mice. Initially, three specific compounds will be studied: the radioprotector S-2-(3- aminopropylamino) ethylphosphorothioate or WR-2721, the radiosensitizer 5-bromo-2'-deoxycyctidine or BCdR, and the anticoagulant warfarin. These drugs will be tested under different conditions. WR-2721 and warfarin will be applied systemically, the former with the object of differentially radioprotecting normal tissues, the latter with the object of reducing metastases, increasing tumor blood flow, and preventing certain late effects. BCdR will be infused intravenously with the object of differentially radiosensitizing pulmonary metastases compared to the normal lung tissue.